There are many kinds of laser alignment devices, which project laser beams by laser generators to mark lines. One such device is designed by U.S. Tool Co. (U.S. Patent Application Publication No. US2002/0178596A1), which can project a line of fixed orientation. Another such device is marketed by U.S. CTB/Berger, which can project a horizontal line and a plumb line decussate to each other on walls perpendicular to the direction of propagation of the laser. The former can merely project a line parallel to the baseplane of its pedestal; the latter can form two lines vertical with each other, but there is a disadvantage that two laser generators are needed, and as the switch is turned on, required or not, the two laser generators project beams simultaneously, thereby causing much more power consumption.